At present, molds are widely used for manufacturing glass optical articles, plastic articles, industrial parts, etc. With the development of the digital cameras, video recorders, compact disc players, their construction articles and glass optical articles are in increasing demand. Generally, these construction articles and glass optical articles are made through a direct press-molding process or an injection-molding process.
A core insert is one of the most important parts of a mold. During the press-molding process or the injection-molding process, the raw material is likely to directly adhere to a molding surface of the core insert, so it is necessary for the core insert to have characteristics such as excellent hardness, good heat resistance and wear resistance, etc.
Several criteria that should be considered in making the core insert are listed below:    (1) the core insert formed should be rigid and hard enough so that the mold cannot be damaged by scratching and can withstand high temperatures;    (2) the core insert formed should be highly resistant to deformation or cracking even after repeated heat shock;    (3) the core insert formed should not react with or adhere to the raw material at high temperatures;    (4) the material of the core insert should be highly resistant to oxidization at high temperatures;    (5) the core insert formed should have good machinability, high precision, and a smooth molding surface; and    (6) the manufacturing process using the core insert should be cost-effective.
Referring to FIG. 4, a typical core insert 10 is shown. The core insert 10 only includes a block. The block defines a smooth molding surface 12 and a number of sidewalls 14 adjacent to the molding surface 12. However, after long time reduplicative molding process, the smooth molding surface 12 is likely to become abraded and corroded. The worst abrasion occurs on or near joins between the molding surface 12 and the sidewalls 14. Thus, the ability of the core insert 10 to produce precision products decreases over time.
What is needed, therefore, is a core insert with good corrosion resistance, good wear resistance, and a method for manufacturing the core insert.